1. Field of the Invention
The present invention relates to a calibration apparatus to be used for a calibration of a sensor for detecting a rotational speed, a calibration method for the sensor, and a manufacturing method for an electronic device which uses the calibration method.
2. Description of the Related Art
There have been proposed various electronic devices, such as a cellular phone and a controller of a consumer game machine, which are provided with a sensor (such as a gyroscope) for detecting a rotational speed. According to such electronic devices, when a user performs an action such as changing an orientation of the electronic device, it is possible to detect the action by using an output from the sensor.
With regard to the sensor, individual sensors have different output characteristics due to individual differences therebetween. Therefore, a calibration for examining the output characteristic of the sensor is performed on the individual electronic devices incorporating the sensor at the time of factory shipment or other such occasions. Specifically, for example, in a case of a three-axis gyroscope for detecting an angular velocity of rotation with each of three reference axes perpendicular to one another used as a center, the calibration is performed by causing the electronic device to rotate with each of those reference axes as the center at a fixed rotational speed and acquiring an output value of the gyroscope. To perform such a calibration, there is proposed a calibration apparatus that can hold the electronic device and cause the electronic device to rotate at a constant speed (see, for example, “1573P Series Three-Axis Position and Rate Table System”, [online], 2010, [retrieved on Oct. 25, 2010], the Internet <http://www.ideal-aerosmith.com/motion/1573P.aspx> (hereinafter, referred to as “Non-patent Document 1”)).
In a case where the above-mentioned calibration apparatus is provided with only one motor that can cause the electronic device to rotate at a constant rotational speed, in order to perform a calibration of the sensor in terms of each of a plurality of reference axes thereof, a measurement needs to be performed by the following procedure. That is, the measurement is repeatedly performed a plurality of times while changing the orientation with which the electronic device is fixed to the calibration apparatus such that a rotation axis of the rotation caused by a motor coincides with each of the plurality of reference axes of the sensor. However, it takes much time and labor to perform the measurement a plurality of times while the electronic device is thus fixed to the calibration apparatus again and again. Meanwhile, as in Non-patent Document 1, in the case where the calibration apparatus is provided with a plurality of motors that can cause the electronic device to rotate at the constant rotational speed, if the electronic device is fixed to the calibration apparatus with such an orientation that the plurality of reference axes of the sensor coincide with a plurality of rotation axes of the calibration apparatus, without fixing the electronic device again thereafter, it is possible to cause the electronic device to rotate with each of the plurality of rotation axes as the center at the constant rotational speed and perform the calibration. However, such a motor that can realize control of the rotation at the constant rotational speed with high precision tends to be more expensive and larger in scale than the motor that cannot perform such control, and hence providing such a plurality of motors leads to an increase in production cost of the calibration apparatus and an increase in scale of the calibration apparatus.